This invention concerns an improved weighing hopper for use generally with a combination weighing system. Such a combination weighing system is disclosed in U.S. patent application Ser. No. 126,915, filed Nov. 30, 1987, and entitled "Method and Apparatus for Linear Combination Weighing," now U.S. Pat. No. 4,821,820, issued Apr. 18, 1989.
This combination weighing system includes a series of in-line transfer conveyors. Each transfer conveyor includes a series of volumetric cups designed to receive and hold a product charge. A scale and associated weighing hopper are provided at the distal end of each transfer conveyor. Each transfer conveyor is advanced in stepped fashion so as to deliver a product charge from one volumetric cup at any single time to the associated weighing hopper. Once the product charge is delivered to the weighing hopper, the weight of the charge is registered by a control unit. The control unit scans various combinations of scales, calculates the total weight of product in the combinations and selects the first combination that falls within an acceptable range above the target weight. Individual product charges are then dumped from the selected weighing hoppers into waiting receptacles for subsequent handling.
The above-described combination weighing system can be specially adapted for use with a sticky product, such as beef cubes or other meat product. The weighing hoppers include two rotary doors, each containing a series of support panels. When support panels on the opposing rotary doors are extending toward each other, a product charge may be received and held within the weighing hopper. When a hopper is selected for discharge the rotary doors are actuated. As the associated support panels of the doors are rotated, the product charge is released into a waiting receptacle.
As should be appreciated, the continuous handling of a sticky product over a number of operating cycles results in a gradual increase in tallow and other product residue on the apparatus components. The combination weighing apparatus disclosed in the above-cited patent application addresses this problem. The apparatus is designed to provide minimal surface contact between the apparatus and product during handling and minimal product transfers throughout weighing and delivering operations. In addition, a liquid washing unit including a spray jet is provided to wash residue from the volumetric cups during system operation. Since this cleaning is completed during system operation, the need to shut the system down for this purpose is greatly reduced, and overall productivity is effectively increased. Furthermore, the above-described invention teaches the use of non-stick surfaces on all components which handle the product.
Despite the effective use of these expedients, it is desirable to further reduce the build-up of residue including tallow and other product matter within the weighing hopper.
More specifically, as the residue builds up over time it effects the accurate weighing of product charges. In particular, with each operating cycle, more and more of the measured product charge weight is actually the weight of the residue remaining in the hopper. This complicates the weighing process as unless a new tare weight is determined after each product discharge, the next product charge weight is increasingly inaccurate. Once product sticks to the hopper surfaces, more product sticks to that product and the inaccuracy accelerates geometrically. Eventually, the inaccuracy becomes so great so as to cause a significant reduction in the total weight of the actual product being delivered to a particular receptacle. This is particularly true since a number of product charges from different hoppers are used to make the target weight. Thus, the effect is further multiplied and a product weight well below the target weight may actually be delivered. This, of course, adversely effects the overall portion weight control quality of the product.
The sticky product residue also slows the flow of product from the hopper. This, of course, adversely effects the overall operating efficiency of the apparatus. In severe cases, it may even cause at least a portion of the product charge to be delivered so late as to not be directed into the desired receptacle. Further, once the tallow builds up to a sufficient weight, a glob of tallow may actually be delivered to a receptacle with the product charge. Both of these matters, of course, have a further undesirable effect on product quality.
A need is, therefore, identified to further reduce the build-up of residue including tallow in the weighing hopper. This advantageously should be accomplished continuously during the weighing and delivery operation to minimize system down time for cleaning. The concern must also be addressed without adversely affecting the ability of the weighing hopper to receive, accurately weigh and quickly discharge the handled product.